Digital timers



y 1962 s. G. HUGHES 3,035,190

DIGITAL TIMERS Filed Nov. 27. 1959 INVENTOR STANLEY G. HUGHES BY 75. W

HTS ATTORNEY.

States Unite The present invention relates to a digital timing device and more particularly to a digital timer for converting balance wheel oscillations to timed electrical pulses.

Generally, a timer is a form of clock or time keeping device which, like a stop watch, can be started at some particular instant and after a prescribed time interval, will cause a switch closure to be effected. Accordingly, a timer consists of an energy source, a time-rate generator and means of recording elapsed time and to effect switch closure at the completion of a preset elapsed time.

Time-rate generators are generally mechanical or electrical wherein the mechanical form may consist of a periodic rotation of a balance wheel and hairspring. The RC circuit is a typical electrical time-rate generator in which electrical charge is accumulated on a condenser as .a function of time. A disadvantage of this is that the timing accuracy is dependent on the constancy of the power supply and the RC values. A crystal oscillator is another form of an electrical time-rate generator, but the frequency is high and has to be divided before mechanical counters can be effectively driven.

The optimum means of recording elapsed time is believed to be based upon a relatively large digital or step motion. To understand the advantage of digital motion, consider a typical non-digital elapsed time recorder which consists of a rotating cam. When the cam rotates; through a prescribed angle corresponding to a prescribed elapsed time, the camming surface closes a switch. With digital motion, position changes discretely each timing increment. Information is not available in such a device regarding the elapsed time between increments but the sudden jump-rotation at each increment provides a precise indication of the total number of increments that have.

elapsed. On the other hand, with a continually moving cam, there is always some timing error since the angle of rotation cannot be precisely determined. Consequently, a more efficient and highly useful timer would be a unique combination of the optimum timer elements, that is, an electrical power source, a balance wheel and a hair-spring, and a means for recording digital motion.

A typical prior art timer .consists of a chronometrically governed DC. motor which has a shaft which rotates at a uniform speed. Such a timer is unduly complicated due to the use of the motor and reduction gearing. Such a timer also is inaccurate when first actuated due to motor inertia. For operation at high speeds over relatively long time intervals such a timer requires relatively large switch closing cams.

An object of the present invention is the provision of a digital timer without complex motion transmission means which would increase the cost and reduce the efiiciency thereof, having high speed motion at critical time intervals, during which time intervals information is not required.

Another object is to provide a compact digital timer which can be started at a particular instant and will operate for a given time period and then effect a switch closure at the completion of the given interval.

In carrying out the invention in one form thereof, a voltage source supplies a current through a counter arm solenoid, a kicker arm solenoid and a balance wheel contact to ground, by closing a starter switch. The kicker arm solenoid then attracts a kicker arm which propels the balance wheel, thus breaking the circuit through the balance wheel contact to ground and making a second ice circuit to ground through the kicker arm. This second kicker arm ground permits the current to continue to flow through both the solenoids attracting a counter arm to the counter arm solenoid which breaks a reset switch disconnecting the voltage source from the solenoids. The counter arm motion drives a counter ratchet registering a count by advancing its motion one tooth. Both the arms then return to their initial position, breaking the circuit to ground through the kicker arm and closing the reset switch. When the balance wheel returns to its initial position after a constant period of time determined by the natural frequency of the balance wheel-hair spring system, the circuit to ground through the balance wheel arm is recl-osed such that this cycle is repeated. The cycle repeats itself until the counter ratchet registers a preselected number of counts rotating a timer cam and actuating a switch indicating the end of one complete timing interval. The features of the invention which are believed to be novel are set forth with particularity in the appended claims. The invention itself, together with further objects and advantages, may best be understood by reference to the following description when taken in connection with the accompanying drawing which illustrates a schematic View of a preferred embodiment of the invention.

Referring now to the drawing, there is illustrated a preferred embodiment of the invention. The counter portion, which is outlined in general by the dashed line 10, will be described first. The counter 10' consists of a counterarm 11 pivoted about a support 12 to drive a counter ratchet 13 by means of an extension 14 on counter arm 11. Counter ratchet 13 is mounted on an axle 15 for rotation. A timing cam 16 is also mounted on axle 15 for rotation with ratchet 13. Timer cam 16 has an indentation 17 for receipt of a cam wheel 18 after the cam 16 had rotated through each preset timing interval. The wheel 18 is spring biased toward the cam 16 by means of a spring 19 which isbi-ased in compression against a support 2% on one extremity and a circular plate 21 at its other extremity.

, The cam wheel 18 is connected to circular plate 21 by means of a yoke 22 and an axle 23. This entire cam wheel is biased by spring 19 to move along the axis of the rod 24, such that when wheel 18 enters indentation 17 at the end of a timing period, contacts 25 are connected by the contact arm 26 to complete a series circuit between voltage source 27 and load 28 which are connected in series across contacts 25.

A drive for counter arm 11 is provided by a counter arm solenoid 29. Counter arm d1 also has on its extremity opposite support 12 a mechanical contact button 30 for driving arm 31 down to open the normally closed reset switch contacts 32 by depressing reset switch contact arm 33. Contact arm 33 is kept normally closed when not driven down by counter arm 11 by means of a spring 34 acting against contact arm 33 and a support 35.

A source of potential 36 for operating the timer is connected between ground and the contact 32 remote from solenoid 29. Thus when contact arm 33 is in its normally closed position, source of potential 36 is connected by means of lead 37 to one side of solenoid 29. The other side of solenoid 29', or lead 38, is connected to one side of a kicker arm solenoid 39.

Solenoid '39 is associated with a kicker arm 40 which is pivoted to rotate about the axis of axle 41. Kicker arm 40 is spring-biased away from solenoid 39 by means of a spring 42 connected between kicker arm 40 and a support point 43. Spring 42 biases kicker arm 40 against stop 44.

The kicker arm 40 is electrically conducting and when it is attracted to solenoid 39 it will make electrical contact through the arm 40 and contact 45 on one end of arm 40 over lead 46 to ground. The other end of kicker arm 40, pivoted around the axis of axle 41, contains a contact arm 47 which is a leaf spring slightly biased against an extension 48 on balance wheel 49. Balance wheel 49 is mounted on an axle 50 which is also provided with a spring 51 which together with balance wheel 49 constitutes a balance wheel-hairspring system having a given period of oscillation which may be utilized for timing purposes. The extension 48, balance wheel 49 and axle 50 are all electrically conducting and are connected from axle 59 by a lead 52 to ground.

The timer may be actuated by closing a switch 53 which is connected between source of potential 36 and the contact 32 remote from solenoid 29. When switch 53 is closed the operating cycle of the timer is initiated. This cycle is as follows:

Upon closing switch 53, source of potential 36 is connected through normally closed contacts 32, solenoid 29, solenoid 39, kicker arm 40, contact arm 47 extension 48, balance wheel 49 and axle 50 to ground through lead 52. The resulting current serves to attract both kicker arm 40 and counter arm 11 to their respective solenoids 39 and 29. The motion of kicker arm 40, transmitted through contact arm 47 and extension 48, serves to rotate balance wheel 49 so as to carry extension 48 away from the arm 47 breaking thecontact between it and extension 48.

This interruption in the circuit previously described would normally cause the current through the solenoids 29 and 39 to cease flowing. However, the motion of the kicker arm also makes contact 45 through the kicker arm 40 to ground over lead 46 permitting the current through the solenoids 29 and 39 to continue flowing.

The current will then continue flowing until counter arm 11 depresses and rotates counter ratchet 13 one tooth by means of extension 14. When the counter ratchet 13 is rotated, counter arm 11 also breaks the circuit across terminals32 by depressing rod 31 by means of contact 30, depressing contact arm 33 and breaking the reset switch contact. The current path from potential source 36 to ground through solenoids 29 and 39 is thenbroken and both counter arm 11 and kicker arm 40 are allowed to return to their initial position reclosing reset switch contacts 32.

The time constants of these mechanically moving parts are so designed that counter arm 11 and kicker arm 40 will have returned to their initial positions before balance wheel 49 has rotated through one half period of the natural frequency of the balance wheel 49 and spring 51 combination, and recontacted arm 47 by means of extension 48. When this recontact is made, the initial conditions prevail and the cycle will repeat itself. This repetition will continue until counter ratchet 13 has rotated sufficiently to carry timing cam 16 around so that cam wheel 18 will snap into indentation 17 making contact across contacts 25 by means of contact arm 26 and indicating a completion of the timing interval. The length of the timing interval can be controlled by the initial setting of ratchet 13 and timer cam 16 with respect to indentation 17.

Supports 12, 20, 35 and 43, axles 15, 41 and 50, solenoids 29 and 39 and stop 44 are all parts of or are mounted on a base (not illustrated). The magnetic circuits are completed through the base structure. The kicker arm 40 may be made of a soft iron to be both magnetic and electrically conductive. A material with a squarer hysteresis loop may be employed to minimize the effect of current variations above saturation on the 4 magnetizing force and resultant strength of the kick imparted to kicker arm 40. The base structure magnetic and electrical circuits may be laminated to reduce eddy current losses and provide a more eflicient magnet.

An isochronous spring may be employed for spring 51 to minimize variations in natural frequency of the balance wheel spring system due to amplitude variations.

, While a particular embodiment of the invention has been described it will be understood of course that it is not intended to limit the invention thereto, since many modifications may be made and that it is therefore contemplated by the appended claims to cover any such modifications as fall within the true spirit and scope of the invention.

What is claimed as new and desired to be secured by Letters Patent of the United States is:

l. A digital timer comprising a digital electromechanical counter means, a balance wheel-spring oscillatory system having a balance wheel with a given natural frequency, a kicker arm system having a kicker arm, said kicker arm contacting said balance wheel to supply it with the necessary energy for oscillation, and means electrically connecting said kicker arm system between said counter means and said oscillatory system for controlling the counting rate of said counter means by said natural frequency. 7

2. A digital timer comprising a digital electromechanical counter means, a balance wheel-spring oscillatory system having a balance wheel and an isochronous spring mounted on a common axle and having a given natural frequency, a kicker arm system having a kicker arm, said kicker arm contacting said balance Wheel to supply it with the necessary energy for oscillation, and means electrically connecting said kicker arm system between said counter means and said oscillatory system for controlling the counting rate of said counter means by said natural frequency.

3. A digital timer comprising a base, a magnetic counter arm pivotally mounted on said base, a counter arm solenoid mounted on said base and positioned to attract said counter arm, a normally closed reset switch cooperatively associated with said counter arm to open said switch when said counter arm is attracted by said counter arm solenoid, a mechanical digital counter having a counter ratchet driven by said counter arm, a magnetic and electrically conducting kicker arm pivotally mounted on said base, a kicker arm solenoid mounted on said base and positioned to attract said kicker arm, a normally open kicker arm ground contact cooperatively associated with said kicker arm to close when said kicker arm is attracted by said kicker arm solenoid, an electrically conductive balance wheel mounted on an electrically conductive and grounded axle, a spring cooperating with said axle to form a balance wheel-spring oscillatory system, said kicker arm being biased against said balance wheel to cause it to oscillate and break contact with said kicker arm when said kicker arm is attracted by said kicker arm solenoid and a source of potential and a switch connected in series from ground through said reset switch, said counter solenoid and said kicker solenoid to said kicker arm.

References Qited in the file of this patent UNITED STATES PATENTS 1,702,411 Olsem Feb. 19, 1929 

